The hypnotic effect of propofol in the medial preoptic area of the rat.

Recent introduction of the intravenous anesthetic propofol as an ICU sedative has allowed a deeply sedated state to be maintained for extended periods in the ICU without delays in emergence. Although such sedation has been advocated to promote physiologic sleep, little evidence exists to support such a strategy. To explore propofol's effect on sleep regulation, we administered propofol directly into the medial preoptic area (MPA) of the rat, an anatomic site where administration of other sedatives (triazolam and phenobarbital) also induce sleep. We performed three two-hour sleep studies in the daytime with the lights on following the administration of propofol (8 ng or 40 ng) or vehicle (intralipid). The higher dose of propofol significantly reduced sleep latency and increased nonREM and total sleep times when compared to vehicle. REM sleep times, intermittent waking times and number of transitions were not altered. Mean nonREM sleep bout length was increased significantly at the higher dose. These findings suggest that propofol may enhance sleep by acting at a hypothalamic site.